The invention relates to an electric machine with means for guiding cooling air fed into the machine interior from the outside.
An electric machine of the above-described type is known having a machine housing including end shields, a lamination bundle carrying a stator winding with winding heads and received in the machine housing and a rotor also received in the machine housing so as to cooperate magnetically with the lamination bundle. The machine housing is provided with at least one inlet and outlet opening for cooling air from the exterior to carry away heat dissipated in the interior during operation of the machine.
In so-called dynamos in motor vehicles it is drive shaft of the generator which direct a flow of air through the machine to carry away the heat losses generated in the generator. The internal ventilators are arranged in such a way that the cooling air delivered by them flows outward over and past the winding heads, so that the heat layer around the winding heads is disrupted. This arrangement does improve the efficiency of the cooling compared with machines having external ventilators, but it poses problems with respect to aerodynamic noise in high-speed machines. To eliminate this problem, liquid-cooled generators have been used in which the housing surface at the stator, at the end shields and at the cooling bodies of the rectifier elements integrated in the generator are cooled with water or oil. The coolant is delivered by pumps and flows through ducts provided for this purpose at the surface of the machine, absorbs the heat losses, is cooled again and finally guided back to the pump. In most cases, this cooling circuit is a closed system which is completely sealed from the outside. The electrically conducting parts of the machine must be electrically insulated, particularly when water is used as coolant. However, the effectiveness of the cooling is substantially reduced by the insulating layer. Because of the expensive machining, the sealing which is required in great changes in temperature, and the necessary feeding and conducting away of the coolant, such systems are only used where no other possibility exists.
Finally, a separately cooled electric machine is known from DE 3303148 A1 in which inlet openings for the cooling air are provided on a front side and air outlet openings, from which the air heated by the heat losses of the machine escape, are provided on the opposite front side. The cooling air flows through the electric machine in the axial direction according to the laws of flow and escapes into the atmosphere. Because of narrow air gaps, sharp changes in cross section, and dead zones, a good cooling efficiency cannot be achieved in such cooling systems and, moreover, considerable aerodynamic noise also occurs in high-speed machines.
It is attempted with the solution according to the invention to improve the air guidance inside the machine in such a way that it flows as intensively as possible around the areas of the machine where most of the heat losses are generated.